1. Field of the Invention
The present invention relates to an image processing apparatus, and more particularly, to an image processing apparatus comprising means for judging whether each pixel of image data is included in a first area of pseudo half-tone image or a second area of non-half-tone image.
2. Description of the Prior Art
In a conventional facsimile apparatus, in order to transmit an image signal through a public telephone line, a transmitter converts image data of non-half-tone image such as characters into binary image data of non-half-tone image by binarizing them using a predetermined threshold value and then transmits the converted binary image data to a receiver of the other party, and also the transmitter converts multi-value image data of half-tone-image into binary image data of pseudo half-tone image by binarizing them using a dither method and then transmits the converted binary image data to the receiver of the other party. It is to be noted that the multi-value image data means image data of multi-gradation stages in the specification. On the-other hand, the receiver of the other party performs different processes depending on the kind of the image of the received image data such as non-half-tone image, pseudo half-tone image or the like. Namely, it is necessary for the receiver to perform the following processes:
(a) a process for extracting each kind of binary image data; PA1 (b) a process for switching over the method for converting the pixel density thereof; and PA1 (c) a process for switching over the decoding method such as the method for compressing image data or the like. PA1 (a) setting a mask for surrounding a plurality of pixels including a specified pixel; PA1 (b) taking out a pixel pattern formed based on values of a plurality of pixels within the mask; PA1 (c) generating an image area signal corresponding to the above-mentioned pixel pattern according to a table of image area signals on the pixel patterns previously stored in a storage unit dividing all the pixel patterns which may be caused into the dot photograph area and the document area; and PA1 (d) outputting the generated image area signal as the image area signal corresponding to the specified pixel. Concretely, the respective pixel patterns are previously stored in a table ROM by dividing the pixel pattern into the dot photograph area and the document area, and when an image signal to be processed is inputted to an address terminal of the table ROM, resulting in the image area signal in the data terminal of the table ROM. PA1 (1) After dividing binary image data into respective blocks, a number of black pixels within each block is counted, a density level of each block is presumed based on the number of black pixels, and then, multi-value image data are recovered based on the presumed density level thereof. PA1 (2) After dividing binary image data into respective unit areas, a number of black pixels within each unit area is counted, and there is obtained the dispersion of the number of black pixels within a predetermined block area composed of not only a specified unit area but also a predetermined number of unit areas adjacent to the specified unit area. Then, when the dispersion thereof is relatively small, an arrangement of black pixels is obtained using a density matrix pattern having a relatively larger size, and then, multi-value image data are recovered based on the arrangement of black pixels. On the other hand, when the dispersion thereof is relatively large, an arrangement of black pixels is obtained using a density matrix pattern having a relatively small size, and then, multi-value image data are recovered based on the arrangement of black pixels. PA1 (3) There is prepared a scanning opening having a size of N.times.N pixels for binary image data, a number of black pixels within each scanning opening is counted shifting the scanning opening by one pixel. Thereafter, the counted number of black pixels is set as a density level, sequentially, and then, multi-value image data are recovered based on the set density level. This method corresponds to a convolution process for binary image data using a spatial filter comprising all the pixels of one or black within a 4.times.4 window. PA1 (a) image identifying means for detecting presence or non-presence of a periodicity of pixel information and the period thereof based on a distribution of pixel information composed of an inputted pseudo half-tone image; PA1 (b) change in density detecting means for detecting a change in the density of the pixel information; and PA1 (c) smoothing processing means for performing a smoothing process using a window having an opening size corresponding to the detected period for a portion where the density gradually changes which is detected by the change in density detecting means, for performing a smoothing process using a window having an opening size smaller than the detected period for a portion where the density often changes many times, and for performing a smoothing process using a window having a predetermined minimum opening size for a portion where there is detected no periodicity, thereby recovering and outputting multi-value image corresponding to the inputted pseudo half-tone image. PA1 image area judgment means for performing an image area judgment process for judging whether each pixel of said inputted binary image data is included in said pseudo half-tone area or said non-half-tone area, based on said binary image data located in a predetermined first area including a plurality of pixels which includes a specified pixel and a plurality of pixels located in the periphery of said specified pixel and which are selected among said inputted binary image data; PA1 first judgment means for judging what is the kind of minor pixels in said first area based on said binary image data located in said first area; PA1 second judgment means for judging whether or not at least one of the minor pixels judged by said first judgment means is included in a predetermined second area which is located within said first area and which is smaller than said first area; and PA1 control means for invalidating result data of said image area judgment process with respect to said specified pixel when said second judgment means judges that none of the minor pixels is included in said second area. PA1 edge emphasis means for performing an edge emphasis process for emphasizing a density difference between a specified pixel and each of a plurality of pixels located in the periphery of said specified pixel; and PA1 prohibition means for prohibiting said edge emphasis process from being performed by said edge emphasis means, when a ratio of a number of white pixels to a number of black pixels which are located in a predetermined area including said specified pixel is larger than a first threshold value smaller than one and is smaller than a second threshold value larger than one. PA1 judgment means for calculating a judgment value representing at least one of a degree of a predetermined pseudo half-tone image and a degree of a predetermined non-half-tone image of each specified pixel of said inputted binary image data based on said binary image data; PA1 first recovery means for recovering binary image data of said specified pixel into multi-value image data using a first recovery process for said predetermined pseudo half-tone image; PA1 second recovery means for recovering binary image data of said specified pixel into multi-value image data using a second recovery process for said predetermined non-half-tone image based on said inputted binary image data; and PA1 mixing means for mixing said multi-value image data recovered by said first recovery means with said multi-value image data recovered by said second recovery means with a mixing ratio corresponding to said judgment value calculated by said judgment means and outputting said mixed multi-value image data.
Therefore, it is necessary to automatically judge whether or not the received image data are binary image data of non-half-tone image or binary image data of pseudo half-tone image, and there is disclosed in the Japanese Patent examined publication No. 63-11832, a method for judging the kind of the received image data and generating an image area signal having the judgment result (referred to as a first conventional method hereinafter). The first conventional method is provided for judging whether or not respective pixels of an image signal having both of a dot photograph area and a document area of characters are included in the dot photograph area or the document area, and for generating an image area signal for representing the judged image area. Namely, the first conventional method includes the following steps:
Further, there is suggested in Yoshinobu MITA et al, "Higher fine multi-value recovery of binary image by Neural Network", Japan Hard copy, '90, NIP-24, pp 233-236, 1990, an apparatus for automatically judging whether or not inputted binary image data are binary image data of non-half-tone image or binary image data of pseudo half-tone image (referred to as a second conventional apparatus hereinafter). In the second conventional apparatus, by using a back propagation method for Neural Network, there is performed not only a process for converting inputted binary image data into multi-value image data using a Neural Network but also a process for dividing inputted binary image data into predetermined kinds of image area and for converting them into multi-value image data depending on the divided image area using the Neural Network. The Neural Network of the second conventional apparatus has a three-layer structure comprising an input layer, an intermediate layer and an output layer. In the input layer, there are provided a number of units corresponding to a number of pixels included in a window provided close to a specified pixel, and there is provided in the output layer one unit for outputting multi-value image data.
However, in the first conventional method, since there is provided the pixel pattern table ROM for judging image areas, as the area to be judged for area judgment increases, the manufacturing cost thereof increases. Further, in the second conventional apparatus, the composition of the apparatus is complicated, and the processing speed is extremely low.
Further, when there is within a window for the area judgment, for example, an end of a line-shaped image including the same kind of pixels which are smaller pixels within an area for the area judgment, there is a possibility of erroneously judging the image areas in the conventional method and apparatus.
Furthermore, in the case of judging whether binary image data of a specified pixel are binary image data of a half-tone image or binary image data of a non-half-tone image based on an adjacent state between respective pixels located within an area for the area judgment, there is a possibility of erroneously judging that binary pseudo half-tone image data binarized by a Fattening type dither binarizing method are binary image data of a non-half-tone image.
Furthermore, in a conventional facsimile apparatus, in order to transmit an image signal through a public telephone line, a transmitter converts a half-tone image such as a photograph image or the like into binary image data of pseudo half-tone image by binarizing them using a dither method or the like, and then, transmits the converted image data to a receiver of the other party. On the other hand, the receiver recovers multi-value image data from the received binary image data of pseudo half-tone.
Further, recently, there has been put into practice a color laser printer for recording an image of multi-value image data at a high speed and with a high resolution, however, there have been widely used binary printers for recording binary image data, generally. In order to store multi-value image data in a storage unit, it is necessary to provide the storage unit having a relatively large capacity.
In order to solve the above problems, the following method is suggested. Namely, the multi-value image data are converted into binary image data, and then, the converted binary image data are stored in the storage unit. Furthermore, upon processing the binary image data or recording the binary image data, after reading out the above binary image data from the storage unit, multi-value image data are recovered from the read binary image data.
Furthermore, there is disclosed in the Japanese Patent laid-open publication No. 62-114377, an image processing method for converting binary image data of pseudo half-tone image into multi-value image data (referred to as a third conventional method hereinafter). In this publication, the following three methods are suggested.
Further, the above-mentioned publication of the third conventional method discloses as follows: simultaneously when performing (3) the convolution process, an image emphasis process is performed using a Laplacian filter for performing a filtering process by multiplying binary image data of a specified pixel by four so as to obtain a first product, multiplying four binary image data of the peripheral pixels in the main scan and subscan directions by (-1) so as to obtain a second product and adding the first product to the second product.
Furthermore, there has been known to those skilled in the art, a conventional method for multi-value image data corresponding to the original image data based on a smoothed value and an edge emphasis value (referred to as a fourth conventional method hereinafter). Namely, a smoothing process is performed for binary image data within the window as described in the above-mentioned process (1) so as to calculate a smoothed value therefor. On the other hand, after calculating the edge emphasis amount within the window, multi-value image data corresponding to the original image data are recovered based on the calculated smoothed value and the edge emphasis value.
However, in the third conventional method, upon recovering multi-value image data having, for example, a natural number N or more of gradation stages, it is necessary to recover multi-value image data based on a natural number N or more of pixels. Further, when a recovery process is performed using a window having one side of length larger than an interval of the period of the original binary image data of pseudo half-tone image, a texture of the pseudo half-tone image may influence the recovered image. In order to solve the above-mentioned problems, it is necessary to use a relatively large window, and then, a circuit for counting the number of black pixels within the window becomes large-sized. Further, when there is an edge portion within the above-mentioned window, the edge portion is smoothed by the smoothing process of the third conventional method, so that the original image data may not be often recovered.
As described above, the edge emphasis amount used in the edge emphasis process and the edge judgment amount used upon judging whether or not there is an edge portion can be calculated based on an edge component amount or a relative amount of the edge component which is detected using the above-mentioned Laplacian filter. However, when using the above-mentioned Laplacian filter, a high frequency component amount can not be accurately detected based on an image having a period of (7.times.2) dots, namely, the high frequency components of the edge portion are lowered. Further, since the direction of the edge component can not be detected, the edge component amount having taken the direction thereof into consideration can not be detected. In this case, an image which is not the edge portion may be erroneously detected as an edge portion, or any edge portion may not be detected within an image including an edge portion. Therefore, when recovering multi-value image data based on the edge component amount calculated by the above-mentioned Laplacian filter using the fourth conventional method, multi-value image data corresponding to the original image data can not be recovered.
Further, an edge emphasis circuit for performing an edge emphasis process for relatively high spatial frequency components which are detected by a window having a width of about one pixel used for calculating an edge emphasis amount is essentially provided for performing an edge emphasis process for an image of a fine line. However, when a number of white pixels within a predetermined area including a specified pixel is nearly equal to a number of black pixels within the predetermined area, a particular image pattern of a pseudo half-tone image tends to become a line-shaped image in a manner similar to that of a fine line image. In this case, there is a possibility of erroneously performing an edge emphasis process for the pseudo half-tone image. Then, binary image data can not be accurately recovered into multi-value image data.
Furthermore, when, for example, a conventional area judgment circuit for judging whether or not inputted binary image data are binary image data binarized by a pseudo-half-tone binarizing method or binary image data binarized by a non-half-tone binarizing method using a predetermined threshold value is applied to an image recovery apparatus, there is a possibility of erroneously judging that binary image data of pseudo half-tone image having relatively low spatial frequency components which are binarized by a Fattening type dither method since the area judgment is performed by detecting the particular image pattern for binary image data of a pseudo half-tone image binarized by an error diffusion method or a Bayer type dither method. In this case, the edge emphasis process may be performed for binary image data of a pseudo half-tone image binarized by the Fattening type dither method, and then, the processed image becomes a lattice-shaped image which is completely different from the original image. In other words, the multi-value image data corresponding to the original image can not be accurately recovered.
Further, there is disclosed in the Japanese patent laid-open publication No. 2-165775, an image processing apparatus (referred to as a fifth conventional apparatus hereinafter) for converting binary image data of a pseudo image data into multi-value image data.
The fifth conventional apparatus is characterized in comprising:
Namely, in the fifth conventional apparatus, the pseudo half-tone image are more faithfully recovered by altering the opening size of the window used for the smoothing process according to the detected change in the density of the pixel information and the detected presence or non-presence of the periodicity of the pixel information.
In practice, various kinds of image readers and various kinds of pseudo half-tone binarizing circuits are provided for various kinds of image processes. However, since the fifth conventional apparatus performs the recovery process for multi-value image data by selectively altering the opening size of the window used for the smoothing process according to the detected change in the density of the pixel information and the detected presence or non-presence of the periodicity of the pixel information, the fifth conventional apparatus can not be applied to a recovery process for image data read by various kinds of image reader or for image data of pseudo-half-tone images binarized by various kinds of pseudo half-tone binarizing circuits. Then, there is often caused errors in the above-mentioned detected results and in the results of the area judgments. Therefore, binary image data binarized by a non-half-tone binarizing method using a predetermined threshold value and binary image data binarized by a pseudo half-tone binarizing method can not be faithfully recovered into multi-value image data corresponding to the original image.